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Attenuation - A measure of how of the light injected into an optical fiber actually reaches the other end, usually expressed in decibels per kilometre (dB/km).
Beat-Length - The length over which polarisation rotates through 360° within an optical fiber and therefore a fundamental measure of the polarisation maintaining ability of a polarisation maintaining fiber.
Birefringence - The fundamental principle by which Fibercore HiBi polarisation maintaining fiber works. A birefringent material has distinct indices of refraction.
Chromatic Dispersion - A pulse-broadening and therefore bandwidth-limiting phenomenon which occurs because different wavelengths of light travel at different velocities.
Conversion Efficiency - In an erbium doped fiber amplifier (EDFA), the ratio between the amplified signal output power and the power input from the pump laser.
Concentricity - Core-cladding concentricity is the distance between the geometric centre of the core and the geometric centre of the cladding. Sometimes called 'Eccentricity' or 'Concentricity Error'.
Cut-Off Wavelength - The wavelength at which an optical fiber becomes single-moded. Below cut-off, the fiber will transmit more than one mode. Above cut-off the strength of the guidance is gradually reduced.
EDFA - Erbium-doped fiber amplifier. A device incorporating erbium doped fiber to provide direct amplification of optical signals when pumped at either 980 nm or 1480 nm.
Extinction Ration - In a polarisation maintaining fiber, the ratio between the 'wanted' and 'unwanted' polarisation states, expressed in decibels (dB). Highly dependent upon operating environment.
Fiber Laser - A laser in which the gain-element is a length of rare-earth doped optical fiber.
Fiber Grating - A selective reflector formed by inducing a periodic variation of refractive index within the core of an optical fiber.
FOG - Fiber Optic Gyroscope. A solid-state replacement for the conventional 'spinning mass' gyroscopes used in direction sensing. Incorporates a coil of HiBi PM fiber as the sensing element.
Gain - In an EDFA, the ratio between the amplified signal output and the (un-amplified) signal input, expressed in dB.
H-Parameter - In a PM fiber, the extinction ratio, expressed as a decimal, per unit length. Should not be used to compare fibers because extinction ratio is also determined by environment.
Mode Field Diameter (MFD) - The diameter of the optical field within the fiber, specified at the 1/e or 1/e2 point (the radial point at which the intensity has fallen to 1/e or 1/e2 of its maximum value).
Noise - In an EDFA, typically based on signal to noise ratio in a regime in which signal-spontaneous beat-noise and amplified signal shot-noise dominate.
Numerical Aperture - A measure of the divergence of the light emitted from the fiber, determined by the refractive index difference between the core and the cladding.
Quantum Efficiency - In the EDFA, the actual conversion efficiency, expressed as a percentage of the maximum possible conversion efficiency (equal to the ratio of the pump and signal wavelengths).
Saturation - EDFA performance under conditions of total population inversion which occur at high input powers.
V-Value - Also called 'Normalised Frequency' - The fundamental relationship between numerical aperture, cut-off wavelength and core diameter.
Fiber Specification Notes:
1. The Design Wavelength is the wavelength (or wavelengths) at which the fiber is typically used. In practice, the fiber will transmit the TEM00 mode at wavelengths of up to approximately 200 nm longer than the cut-off wavelength.
2. The Mode Field Diameter is a nominal, calculated value, estimated at the operating wavelength(s) using typical value of numerical aperture and cut-off wavelength.
3. Attenuation is a worst-case value, quoted for the shortest design wavelength.
4. Beat Length is measured at 633 nm for all HB fiber types. To a first approximation, beat-length scales directly with operating wavelength.
5. Background loss is quoted at a minimum point of the spectrum (typically 1100 nm to 1200 nm for the DF1500 series)
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